U.S. Pat. No. 4,707,346 describes doping an SnO—SnO2 system Ta2O5 and/or Nb2O5 using pyrochlore-related compounds for use in thick film resistor compositions.
U.S. Pat. No. 6,534,183 describes compositions useful to prepare transparent electroconductive films. Most of the compositions described therein require the presence of indium oxide. In the broad compositions described (see column 5, lines 13-22 and column 6, lines 2-68), the reference suggests that zinc oxide and relatively small amounts of one or more oxides selected from the group consisting of iridium oxide, rhenium oxide, palladium oxide, vanadium, molybdenum and ruthenium also be added. The reference does not define the phrase “molybdenum oxide.” As is known in the art, molybdenum oxide can have valencies of 2, 3, 4, 5 and 6. In general, where the art refers to “molybdenum oxide”, the oxide “molybdenum trioxide (MoO3) is meant.
SnO2, ZnO2, In2O3, and ITO are known to be useful as transparent conductive coatings (see, e.g., U.S. Pat. Nos. 6,586,101, 6,818,924 and 6,979,435; “Amorphous indium tungsten oxide films prepared by DC magnetron sputtering,” Abe et al, Journal of Materials Science, volume 40, 2005, pages 1611 through 1614; “Chemical and Thin-Film Strategies for New Transparent Conducting Oxides,” Freeman et al, MRS Bulletin, August 2000, pages 45 through 51; “Transparent Conductive Oxides: ITO Replacements,” Coating Materials News, volume 15, Issue 1, March 2005, pages 1 and 3; “Chemical and Structural Factors Governing Transparent Conductivity in Oxides,” Ingram et al, Journal of Electroceramics, volume 13, 2004, pages 167-175; and “Transparent conducting oxide semiconductors for transparent electrodes,” Minami, Semiconductor Science and Technology, volume 20, 2004, pages S35-S44). Transparent conductive films from tungsten or germanium-doped for indium oxide (see U.S. Pat. No. 6,911,163) and from indium oxide doped with ZnO and/or WO3 (see US Patent application publications 2005/0239660 and 2006/0099140, “High electron mobility W-doped In2O3 thin films by pulsed laser deposition,” Newhouse et al, Applied Physics Letters, Volume 87, 2005, pages 112108-1 through 12108-3) are also known. Finally, transparent conducting oxides of In2O3 doped with Ta2O5 are also known (see “Electrical and Optical Properties of New Transparent Conducting Oxide In2O3:Ta Thin Films,” Ju et al, Journal of Korean Physical Society, volume 44, no. 4, 2004, pages 956-961). Finally, Casey et al (“A study of undoped and molybdenum doped, polycrystalline, tin oxide thin films produced by a simple reactive evaporation technique,” J. Phys. D: Appl. Phys., volume 23, pages 1212-1215) describe a technique wherein doping is achieved by placing a molybdenum foil in front of a tin substrate during thin film deposition. The resultant material is apparently a molybdenum oxide-doped tin oxide (see the 5th paragraph in the right column of page 1213).
In order to be commercially useful in flat panel displays as transparent conducting oxide, the film must have an electrical conductivity of at least 103 S/cm and a light transmittance of at least 80%.
For a material or film to be considered as conductor, the resistivity should be less than 10−2 ohm-cm. For a material or film to be considered as a semiconductor, the resistivity should be between 1 and 108 ohm-cm. A material having a resistivity of 1 ohm-cm is considered as something between a conductor and a semiconductor.
Depending on the processing conditions, the film can be either a conductor or a semiconductor. If the film has semiconductor properties, it then can be used as semiconductor layer in transparent electronics applications (e.g., transparent thin-film transistor).